Conventionally, for example, a technique is known in which a molded fiber-reinforced resin product is produced by heating and pressurizing in a molding die sheet-shaped prepreg manufactured by impregnating reinforcement fibers with an uncured thermosetting resin (for example, see Patent Document 1).
For cases where the molded fiber-reinforced resin product has a three-dimensional shape including a curved surface, a technique is also known in which a preform is produced by forming sheet-shaped prepreg into a shape predetermined in consideration of the shape of the final molded product prior to the main molding process for obtaining a desired molded fiber-reinforced resin product.
As a method of obtaining desired preforms, the following method is known (for example, see Patent Document 2).
(i) Heating a laminate of a plurality of prepreg sheets using an infrared heater.
(ii) Bending the prepreg by sandwiching the heated prepreg between preform molds of a male mold and a female mold.
(iii) Cooling the prepreg by blowing air onto the preform molds.
(iv) Opening the preform molds and taking out the prepreg such that the bent shape is maintained.
In addition, a method is also known in which prepreg heated to a predetermined temperature is arranged in a preform mold having a convex shape and the prepreg is formed while being pressed with a rubber film (for example, see Patent Document 3).
Furthermore, in order to suppress occurrence of wrinkles, a method is also known in which a plurality of pattern-cut sheets of prepreg provided with extension portions in their outer periphery are laminated; the prepreg is formed while tension is imparted by tension imparting units installed in a preform forming machine; the extension portions are cut off after the forming; and thus desired preforms are obtained (for example, see Patent Document 4).